The invention relates to improved electric detonators comprising lead-free compositions having the same functionality as the standard lead-based detonators.
Detonators are tiny compact devices that are used where a strong shockwave is needed to initiate larger explosive charges, such as leads or boosters (secondary explosives) via sympathetic detonation; their applications range from explosive munitions to demolition charges. They are frequently incorporated as parts of a larger fuze apparatus which may also include additional pyrotechnic delays and/or booster charges. As such, detonators are essential for a huge number of explosive munitions including grenades, mortars, rockets, artillery rounds, submunitions, etc. The two main types of detonators are stab and electric. Stab detonators (FIG. 1), are initiated by a mechanical force whereas electric detonators (FIG. 2) are initiated by an electrical impulse which causes resistive heating in an embedded metal bridgewire.
A small scale electric detonator is called a “microdet”. One example of a microdet detonator is the M100. Current microdets detonators, such as the M100, are similar to hot wire initiators, where a metal bridgewire is covered with a lead styphnate spot charge. An electrical current heats the bridgewire by voltage that is applied via a firing circuit which ignites the spot charge, lead styphnate (LS) to initiate the ignition material, lead azide (LA), which in turn initiates the output charge, HMX. This detonator is used in all military mortar fuzes such as M734, M759, etc. to further set off the lead to the booster to the main charge explosives. Standard military M100 electric detonators must meet stringent requirements of having an output dent greater than or equal to 0.005″. Typical output dents generated by current electric M100 electric detonators containing lead azide and lead styphnate compositions are between 0.010″ to 0.016″ with all fire parameters of 1.6V at 100 μF capacitor.
Current microdet electric detonators such as M100 contain lead azide and lead styphnate which are toxic. Furthermore, lead azide reacts with copper, zinc or alloys containing such metals, forming other azides that can be highly sensitive and dangerous to handle. In addition, lead-based materials are well established to cause environmental and health related problems. Lead-based materials are cataloged on the EPA Toxic Chemical List (EPA List of 17 Toxic Chemicals); they are additionally regulated under the Clean Air Act as Title II Hazardous Air Pollutants, as well as classified as toxic pollutants under the Clean Water Act, and are on the Superfund list of hazardous substances. Recently, under the Clean Air Act, USEPA (U.S. Environmental Protection Agency) revised the National Ambient Air Quality Standard (NAAQS) to 0.15 μg/m3, which is ten times more stringent than the previous standard. Lead is both an acute and chronic toxin, and the human body has difficulty in removing it once it has been absorbed and dissolved in the blood. Consequently, a chief concern is the absorption of lead by humans from exposure to initiating mix constituents, as well as the combustion by-products of lead based compositions. The health effects of lead are well documented; however, recent studies have shown that there are no safe exposure levels for lead, in particular for children. There is a direct correlation between lead exposure and developmental impacts, including IQ loss (even at the revised lead NAAQS, exposure levels are consistent with an IQ loss of over 2 points), behavioral issues and even hearing loss. Their use during military training and testing deposits heavy metals on munition ranges and can impact sustainable use of these ranges. Manufacturing of any lead-based primary explosives, such as lead azide or lead styphnate, results in the production of significant quantities of highly toxic hazardous waste. Handling and storage of these compounds is also a concern. Thus, a need exists for effective microdet electric detonators that are free of lead components yet produce the same rigorous performance qualities as the standard lead-based detonators.